Aux outboard kicker on a 50' displacement vessel

[Mako]

OP how about going a different direction like a get home drive powered by your generator?

 

[ofer]

OP how about going a different direction like a get home drive powered by your generator?

i like an outboard that will function as emergency steering also.

 

[DNT99611]

i like an outboard that will function as emergency steering also.

I think you should do it and report back

I have been thinking along the same line but on a smaller scale. And with a little slick rigging it could serve as a dandy stern thruster.

 

[rpackard]

I am pretty sure that a 60 hp outboard is more than sufficient to drive you at 4-5 knots. If you could measure (or have manufacturer data) your fuel consumption (in gal/hr) when you power at 4.5k, then you know what power you need. The conversion is 1gal/hr ~18hp.
My Willard 40, 18ton trawler moves at ~4kn (in flat water) when powered by a 7.5hp electric motor. My Willard 30 trawler requires only 12hp at 6knots. If I drove that boat at 4knots I think 5hp would do the job.

Ask a friend with ~ a 12hp outboard to try to tow you and see what speed you reach. At slow speeds the power is quite proportional to the speed. Of course having a very low pitch prop is important.

A hull driven well below its hull speed requires very little power.

 

[mikecambrai]

You don't say what your main engine is, but they are usually so much more rugged and reliable than a twin, and in 60 years properly installed and maintained is usually better than keeping a twin installation. The Prop being on the centre is well away from trouble and with no A frames to worry about a single is so much better.
If you do feel that you need another option, I would install a wing shaft in the E/R with a folding prop and a hydraulic motor attached. Then I would put a 50HP diesel in a convenient corner out of the way. A much more reliable get-you-home system that works.
Outboards on the end of a displacement hull will spend a lot of time racing out of the water.

 

[ofer]

just ordered the Honda BFP60 power thrust with 25" shaft.

the only issue i see is needing a 50' throttle/shift cables. dealer says they only have up to 40'

i also need to figure out where to store the 100 gal gasoline tank. it will be above deck or on the swim step.

don't want to start any flames...are there any rules against storing gasoline on a swim step?

 

[O C Diver]

just ordered the Honda BFP60 power thrust with 25" shaft.

the only issue i see is needing a 50' throttle/shift cables. dealer says they only have up to 40'

i also need to figure out where to store the 100 gal gasoline tank. it will be above deck or on the swim step.

don't want to start any flames...are there any rules against storing gasoline on a swim step?

There are manufacturers that make custom length shift and throttle cables. I bought a set of super easy cables for my charter boat years ago from a company called Rose Marine in Massachusetts.

Regarding the gas tank, I wouldn't want all my eggs in one basket....or fuel. 2 or 3 tanks with their own supply hoses would be my choice.

Ted

 

[Benthic2]

Do you need throttle and shift cables ? If you are using this motor you are going to be going in a long straight line at a constant speed. You would still have some steerage with your main rudder. You don't need to be so maneuverable that you can dock.....if you can get to within 10 yards of the marina, it was a success.....you'll have options from that point.

If you have a crane/boom I am not sure I would even mount it. Put a bracket on your swim platform and leave the outboard in the lazarette until you need it.....which will probably be never.

 

[Circumnavigator]

A data point: 60HP will move Fintry at 4 knots. 300,000+ pounds displacement, 79' long, 75' on the water. That's with a five foot prop. It takes very little power to move a displacement boat at speeds around 0.5 S/L.


As noted above, getting power into the water with a small propeller is hard at slow speeds.


Jim

 

[Mako]

Jim are you referring to pushing Fintry with 60hp being generated by your diesel or via an outboard?

 

[thataway]

Another experience: We lost the transmission going thru the Rue de Brest,France so calm water, LWL 40' Displacement 60,000#.Draft 6 1/2 feet motor sailor. Initially used hard dinghy on the hip with 4.5 hp and achieved 2 knots and steerage way. Inflated 13' inflatable with 25hp and achieved 4.5 to 5 knots. The boat had fine lines and was easy to push.

We also developed experience using the 13' inflatable with the 25 hp outboard as a "Push Boat"--put the bow of the inflatable agains the transom of the larger boat, and found it was an efficient way to push, and had control by maneuvering the inflatable, and able to "steer". We used lines from each side to hold tight against the transom.

I believe that the 60 with large as prop as you can fit, will be the best option.

 

[ofer]

A data point: 60HP will move Fintry at 4 knots. 300,000+ pounds displacement, 79' long, 75' on the water. That's with a five foot prop. It takes very little power to move a displacement boat at speeds around 0.5 S/L.


As noted above, getting power into the water with a small propeller is hard at slow speeds.
Jim

yes the issue is not the HP. at idle my boat travels at 4kts using about 25HP.

I am worried about the prop although the honda power thrust has the largest prop available for that HP.

 

[ofer]

Another experience: We lost the transmission going thru the Rue de Brest,France so calm water, LWL 40' Displacement 60,000#.Draft 6 1/2 feet motor sailor. Initially used hard dinghy on the hip with 4.5 hp and achieved 2 knots and steerage way. Inflated 13' inflatable with 25hp and achieved 4.5 to 5 knots. The boat had fine lines and was easy to push.

We also developed experience using the 13' inflatable with the 25 hp outboard as a "Push Boat"--put the bow of the inflatable agains the transom of the larger boat, and found it was an efficient way to push, and had control by maneuvering the inflatable, and able to "steer". We used lines from each side to hold tight against the transom.

I believe that the 60 with large as prop as you can fit, will be the best option.

that's very encouraging data thanks

 

[ofer]

if i get 4-5kts in calm conditions and am able to move forward at any speed in adverse conditions I will consider this a win.

 

[Circumnavigator]

Jim are you referring to pushing Fintry with 60hp being generated by your diesel or via an outboard?

She has a get home drive which runs off the 60HP hydraulic pump that runs the bow thruster, windlass, and 3" pump. It uses a big bicycle chain to drive the main shaft from a 60HP hydraulic motor. The pump is driven by a Gardner diesel, entirely separate from the CAT 3406 main.


Jim

 

[janice142]

my question is about HP required to move the boat at 4-5 kts

Regarding your issue/desire for an auxiliary propulsion unit. I believe Ted and Sara aboard Manatee have the best solution. They have a cool solution to a main engine failure. First they launch the tender, attach it to their boat (that's the interesting part) then they start the outboard (35hp if memory serves me), turn on the autopilot in the tender... and well, it sure does look about perfect to me.

Eons ago I wrote an article for my website about them/their boat. It has pictures of the set-up which may offer you some ideas for your vessel. Though yours is larger, the KK36 has a lot of windage.

Article: Manatee Moves article on janice142

Good luck Cap'n.

 

[DennisB1]

If you can achieve about 5 knots you need clean flow to the prop. You would want the cavitation plate on the outboard at or slightly below the transom bottom to get good thrust IMO. Look at the wake with the main engine when you are running at 4 - 5 knot to assess if it’s ok with your OB plans.

 

[koliver]

just ordered the Honda BFP60 power thrust with 25" shaft.

the only issue i see is needing a 50' throttle/shift cables. dealer says they only have up to 40'

i also need to figure out where to store the 100 gal gasoline tank. it will be above deck or on the swim step.

don't want to start any flames...are there any rules against storing gasoline on a swim step?

Until now, I have assumed that like your other thread, this is all hypothetical. But now you say you have ordered a 60hp outboard!
Have you already rebuilt your swim step to handle the weight, torque, access? If so, can you post some pictures of the beefier supports. Have you added buoyancy to handle the weight of a big, heavy outboard well aft of your transom?

Speaking of your other thread, is not this outboard part of your get home strategy? Why would you utilize its fuel supply in your diesel engines rather than preserving its get home ability by having a full tank?

 

[ofer]

Until now, I have assumed that like your other thread, this is all hypothetical. But now you say you have ordered a 60hp outboard!
Have you already rebuilt your swim step to handle the weight, torque, access? If so, can you post some pictures of the beefier supports. Have you added buoyancy to handle the weight of a big, heavy outboard well aft of your transom?

I am working on the design of the bracket and swim platform support ideas. it will be strong enough.

I have some experience with aux kicker outboards. I am probably the only one that has a 27HP Yanmar outboard on my 30 foot inboard sportfish.

Speaking of your other thread, is not this outboard part of your get home strategy? Why would you utilize its fuel supply in your diesel engines rather than preserving its get home ability by having a full tank?

the other thread was all else fail scenario....
I am in heavy seas my outboard is not capable of keeping the boat on course...running out of the diesel and i have 100 gal of gas.

I know this will probably not happen considering all the redundant systems i have. although i like to keep all options open.

Thank you for at least reading my posts without criticizing.

 

[ofer]

Regarding your issue/desire for an auxiliary propulsion unit. I believe Ted and Sara aboard Manatee have the best solution. They have a cool solution to a main engine failure. First they launch the tender, attach it to their boat (that's the interesting part) then they start the outboard (35hp if memory serves me), turn on the autopilot in the tender... and well, it sure does look about perfect to me.

Eons ago I wrote an article for my website about them/their boat. It has pictures of the set-up which may offer you some ideas for your vessel. Though yours is larger, the KK36 has a lot of windage.

Article: Manatee Moves article on janice142

Good luck Cap'n.

This would too messy since i am single handed.

 

[BruceK]

She has a get home drive which runs off the 60HP hydraulic pump that runs the bow thruster, windlass, and 3" pump. It uses a big bicycle chain to drive the main shaft from a 60HP hydraulic motor. The pump is driven by a Gardner diesel, entirely separate from the CAT 3406 main.


Jim

Wouldn`t the risk a get home system seeks to overcome be better served with a separate shaft?

 

[DNT99611]

Seems to me that if you want a true get home/emergency system it needs to be totally stand alone. No use of main shaft or steering.
The often made statement of call your tow service does not work in places where they do not offer service. Nor will they work if you need help in minutes not hours.
I spend a lot of time fishing close to rocky shores where the bottom drops straight down so no anchor option. If the main quits no tow service is going to keep me of those rocks. A good running kicker sure feels good in that case.

 

[Jeff F]

Regarding your issue/desire for an auxiliary propulsion unit. I believe Ted and Sara aboard Manatee have the best solution. They have a cool solution to a main engine failure. First they launch the tender, attach it to their boat (that's the interesting part) then they start the outboard (35hp if memory serves me), turn on the autopilot in the tender... and well, it sure does look about perfect to me.

I was thinking about their arrangement just before reading your comment. The tender is attached to the transom and they have guy lines to keep it straight while pushing, and a remote control for the dinghy AP.

 

[ofer]

I was thinking about their arrangement just before reading your comment. The tender is attached to the transom and they have guy lines to keep it straight while pushing, and a remote control for the dinghy AP. View attachment 125152

do we know the HP any type of outboard in the dingy?

 

[ofer]

I was thinking about their arrangement just before reading your comment. The tender is attached to the transom and they have guy lines to keep it straight while pushing, and a remote control for the dinghy AP. View attachment 125152

the dingy can serve as a nice swim step too

 

[Jeff F]

do we know the HP any type of outboard in the dingy?

90 HP these days. I think the tender is always in the water, and normally attached.

 

[ofer]

90 HP. I think the tender is always in the water, and normally attached.

oh crap. i hope my 60 will do the job. although the 60 power thrust has same gearcase and props as the 90.

 

[Gdavid]

I was thinking about their arrangement just before reading your comment. The tender is attached to the transom and they have guy lines to keep it straight while pushing, and a remote control for the dinghy AP. View attachment 125152

This is very similar to the skipjack's skiffs used in the Chesapeake bay. Historically there were (perhaps are) days allocated to sail power dredging and other days push only. They have dedicated inboard powered skiffs that lower from stern mounted davits and then the bow of the skiff wedges against the stern and then block and tackles control the position of the skiff's stern. The whole point of the rules were to make it challenging and prevent over harvesting.

 

[BruceK]

oh crap. i hope my 60 will do the job. although the 60 power thrust has same gearcase and props as the 90.

Maybe check the torque output rather than hp. Mfrs often use the same block for 2 differing hp engines.

 

[ofer]

Maybe check the torque output rather than hp. Mfrs often use the same block for 2 differing hp engines.

the 60 and 60PT have the same engine torque. The PT has a lower gear ratio which would translate to more torque at the prop.